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Chapter 4
Theory of Operation
Analog Input Circuitry
The BNC-2140 has four identical analog input channels.
The BNC-2140 supplies a constant current for IEPE accelerometers
and microphone preamplifiers. Many accelerometers use piezoelectric
materials to generate a charge proportional to the acceleration applied.
These types of accelerometers are susceptible to external noise. A charge
amplifier is embedded within the sensor to reduce the effects of cable
length, noise, and other spurious effects. The BNC-2140 supplies the
constant current required to power the embedded charge amplifier in the
IEPE sensor, so you can use inexpensive cables, such as BNC cables.
Some manufacturers use IEPE signal conditioning to power their
prepolarized microphones. If your application requires a microphone
preamplifier for use with a prepolarized microphone, refer to the
Equipment
If you attach an IEPE-type of accelerometer or microphone preamplifier
to an analog input channel, you must turn on the IEPE power switch and
enable the IEPE circuit for that channel to generate the required current.
The IEPE circuitry of any input channel can be enabled or disabled
independently of any other input channel. When IEPE is disabled, the
connection from the IEPE circuit to that channel breaks and has no effect
on the incoming signal. If IEPE is not required on any of the four input
channels, power off IEPE to de-energize the circuitry. Powering off IEPE
removes noise induced by the circuitry on the incoming signal.
The BNC-2140 allows you to select between DIFF and SE input modes.
You can use IEPE signal conditioning when the inputs are in either mode.
Analog Output
The BNC-2140 has two analog output channels. The BNC-2140 can select
between DIFF and SE outputs.
In DIFF mode, the positive and negative sides of the output channel are
floating. Use DIFF mode when the unit under test has grounded input
terminals. In SE mode, the negative side of the output channel is connected
to AO GND with a 50 Ω resistor.
BNC-2140 User Manual
Artisan Technology Group - Quality Instrumentation ... Guaranteed | (888) 88-SOURCE | www.artisantg.com
section of Chapter 1, Introduction, for supplier information.
4-2
Optional
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